The present invention relates generally to data transmission in communication systems and more specifically to systems and methods for association and uplink adaptation and power control in a relay network.
As used herein, the terms “user agent” and “UA” can refer to wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices or other User Equipment (“UE”) that have telecommunications capabilities. In some embodiments, a UA may refer to a mobile, wireless device. The term “UA” may also refer to devices that have similar capabilities but that are not generally transportable, such as desktop computers, set-top boxes, or network nodes. Throughout the present disclosure the term “UA” is equivalent to the term “UE”.
In traditional wireless telecommunications systems, transmission equipment in a base station or other network node transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). Additional improvements to LTE systems and equipment will eventually result in an LTE advanced (LTE-A) system. As used herein, the phrase “base station” will refer to any component, such as a traditional base station or an LTE or LTE-A base station (including eNBs), that can provide a UA with access to other components in a telecommunications system.
In mobile communication systems such as the E-UTRAN, a base station provides radio access to one or more UAs. The base station comprises a packet scheduler for dynamically scheduling downlink traffic data packet transmissions and granting resources for uplink traffic data packet transmission for all the UAs communicating with the base station. The functions of the scheduler include, among others, dividing the available air interface capacity between UAs, deciding the transport channel to be used for each UA's packet data transmissions, and monitoring packet allocation and over-the-air resource utilization. The scheduler dynamically allocates resources for Physical Downlink Shared CHannel (PDSCH) and grants resources for Physical Uplink Shared CHannel (PUSCH) data transmissions, and sends scheduling information to the UAs through a control channel.
To facilitate communications, a plurality of different communication channels are established between a base station and a UA including, among other channels, a Physical Downlink Control Channel (PDCCH). As the label implies, the PDCCH is a channel that allows the base station to control a UA during downlink data communications. To this end, the PDCCH is used to transmit scheduling or control data packets referred to as Downlink Control Information (DCI) packets to the UA to indicate scheduling to be used by the UA to receive downlink communication traffic packets or transmit uplink communication traffic packets or specific instructions to the UA (e.g. power control commands, an order to perform a random access procedure, or a semi-persistent scheduling activation or deactivation). A separate DCI packet may be transmitted by the base station to the UA for each traffic packet/sub-frame transmission.
In some network implementations, relay nodes (RNs) may be included amongst the various network components to efficiently extend a UA's battery life and increase UA throughput. For example, in some networks, base stations and RNs may work together to transmit the same signal to a UA at the same time. In such a system, the signals transmitted by the base station and RN may combine (i.e., superpose) in the air to provide a stronger signal and thus increase the chance of transmission success. In other networks, base stations and RNs transmit different signals to the UA, which, for example, include different data that is to be communicated to the UA. By transmitting different portions of the data through different base stations and/or RNs, the throughput to the UA may be increased. The use of a combination of base stations and RNs depends on many factors including channel conditions at the UA, available resources, Quality of Service (QoS) requirements, etc. As such, in some network implementations, in a given cell or combination of cells only a subset of available UAs may be serviced with combinations of base stations and RNs.
FIG. 1 is an illustration of a wireless communications network that incorporates base stations and RNs for transmitting data to a UA. Several RNs 100 are positioned around the edges of cells 102 and 104. The network includes several base stations 12 for coordinating network communications, which may include eNBs. The combination of RNs 100 and base stations 12 communicate with UAs 10. In FIG. 1, UA 10a is served by a lone RN 100a. Because RNs 100 are distributed about the edge of cells 102 and 104, UAs 10 can access the network at a higher data rate or lower power consumption by communicating directly with RNs 100 rather than base stations 12.
In a network that includes RNs in combination with base stations, there can be significant difference between the base station's transmission power (e.g., 46 dBm) and an RN's transmission power (e.g. 30 dBm). The difference in transmission power can lead to different coverage areas for both the RNs and base stations. In any network, however, the UA has only a single transmission power for signals transmitted to the RN and/or the base station and the received power for such a signal is dependent on the propagation path between the UA and the RN or the base station. As such, there may be times when the UA receives a stronger downlink (DL) transmission from the base station than from an RN while the RN receives a stronger uplink (UL) UA transmission than the base station. This situation results in an uplink/downlink (UL/DL) imbalance situation. In UL/DL imbalance, on the UL, the best serving node (e.g., base station or RN) may be the one that has the smallest coupling loss (e.g., path loss plus the transmit and receive antenna gains) with the UA while on the DL, the best serving node may be the one that provides the strongest DL received power at the UA (i.e., includes the transmit power of the node besides the coupling loss).